Elongated medical devices such as guide wires, guiding catheters, ultrasonic catheters, atherectomy devices, catheters for radiofrequency (RF) cardiac ablation, etc., are used extensively by interventional cardiologists and interventional radiologists. Elongated medical devices are utilized as well in neuro-surgical, orthopedic, ear-nose-throat, and obstetrical and gynecological procedures, etc. to perform many diagnostic and/or interventional procedures without the need for more traditional surgery. Typically, the elongated medical device is introduced percutaneously, providing access to some remote location within the body, such as, e.g., a coronary artery. In some circumstances, the rotational orientation of the distal end of the medical device is irrelevant, such as with certain ultrasound catheters. In other circumstances, however, the rotational orientation of the distal end of a medical device is very important. For example, catheters used to map the electrical potential of the myocardium (and similar catheters used for cardiac ablation) typically have a distal end portion with a preshaped configuration to facilitate placement of the distal end of the catheter in various positions within the chambers of the heart. Rotational control of such devices is also very important. Shturman has described certain directional rotational atherectomy devices for which control of the rotational orientation of the distal end of the device is important (see, e.g., U.S. Pat. No. 5,360,432).
Common techniques for providing such control of the rotational orientation of a device's distal end have typically relied on the use of wire reinforcement (such as wire braiding) embedded in the device (e.g., in the wall of a catheter). While such reinforcement increases the torque-conveying ability of the device, the efficacy of this technique nevertheless depends on the ability of the device to convey rotation in a 1:1 ratio from the proximal end to the distal end. That is, after inserting the device to the desired location, in order to achieve the desired rotational position, the physician turns the proximal end of the device, and relies on the device's ability to convey that rotation in a 1:1 ratio to the distal end of the device. Thus, a 90.degree. rotation of the proximal end is intended to result in a 90.degree. rotation of the distal end of the device.
In practice, however, this result is more difficult to accomplish. A physician often may be using a relatively thin, flexible device having a length of up to four or five feet, inserted through a sometimes winding or even tortuous path. As a result, a significant amount of friction can be encountered over the length of the device, and the 90.degree. rotation of the proximal end does not always result in a 90.degree. rotation of the distal end. Rather, a lesser degree of rotation (or no rotation at all) occurs at the distal end, with torque building up through the length of the device. Further rotation of the proximal end is required to overcome the friction, but can result in the distal end "whipping" and over-rotating (i.e., once the distal end begins to rotate, since the coefficient of dynamic friction is less than the coefficient of static friction, the built-up torque is released and the distal end of the device rotates the full amount that the proximal end had been rotated, a degree of rotation greater than what the physician intended).
Thus, while reinforcing braids, etc., improve the torque-conveying abilities of such devices, they rely on the theoretical 1:1 rotation ratio (which is difficult to obtain in actual use), and they are still subject to "whip", thus making it difficult to provide the desired degree of control over the rotational orientation of the distal end of the device.
Reinforcing braids also tend to reduce the lateral flexibility of such elongated medical devices and, thus, the ability to track well (over guide wires, for example) through tortuous vasculature.